Natural gas flowing from wells typically contain water vapor along with entrained liquids, such as water droplets and oil droplets. These entrained elements, and particularly entrained water, can cause many problems in pipeline and processing equipment. For this reason, it has long been a common practice to treat the natural gas at or near the well head to remove these materials from the gas before it is passed into a pipeline. Removing water vapor and other impurities helps to prevent clogging of a pipeline with liquid water or liquid hydrocarbons which frequently separate out of gas as it passes through a pipeline due to the lower temperatures existing in the pipeline compared to the temperatures of which the gas naturally exists in the earth. Further, removal of water impurities helps prevent formation of hydrates which can clog a pipeline system. Finally, an important reason for removing water vapor and other contaminates is to prevent corrosion of pipelines, tanks and other components of transportation and processing systems.
Processes for removal of entrained water vapor and other contaminants in natural gas are well known. The most commonly used process employs glycol dehydration. Before treating a gas for glycol dehydration, it is typically passed into a separator where water droplets, along with droplets of hydrocarbon liquids, entrained sand, rust and so forth is separated from the gas stream. Condensable hydrocarbons and water are generally removed by expanding the high pressure gas from a well so that the resultant temperature drop causes condensation of the condensables.
Subsequent dehydration of the gas is most commonly achieved by contacting it with a desiccant liquid that readily absorbs water. The most commonly used desiccant is glycol either in the form of diethylene glycol or triethylene glycol. Water vapor entrained within the gas stream is absorbed by the glycol desiccant, and the desiccant is then regenerated by heating it to drive off the absorbed water. After the desiccant has been heated to regenerate, it is then recycled for use in the dehydration system. Usually, the heat required for regeneration of the liquid desiccant is obtained by burning a portion of the natural gas.
For background information relating to glycol dehydrator systems for treating natural gas, reference may be had to U.S. Pat. Nos. 5,163,981; 5,116,393; 4,375,977 and 4,661,130.
One problem that has existed with glycol dehydrators is that when spent glycol is heated to drive off the entrained water that has been extracted from natural gas, frequently, along with the vapor that is driven off, some aromatic hydrocarbons are also passed into the atmosphere. These aromatic hydrocarbons are considered pollutants. They include benzene, toluene, ethylene and xylene, sometimes referred to in the trade as BTEX. They are environmentally hazardous and are considered carcinogens. These and other deleterious hydrocarbons that can be generated in the process of dehydrating natural gas are collectively referred to as volatile organic compounds, sometimes shortened to VOC's.